Sensing device and electronic device

ABSTRACT

In a sensing device that generates a distance image, a variation in distance measurement accuracy in the distance image is reduced. The sensing device includes a predetermined number of pixel circuits and a voltage control unit. Each of the predetermined number of pixel circuits includes a photoelectric conversion element and a detection circuit. A predetermined reverse bias voltage is applied between an anode and a cathode of the photoelectric conversion element. The detection circuit detects whether a photon is present or absent on the basis of a potential of either the anode or the cathode. The voltage control unit adjusts the reverse bias voltage to a value corresponding to a breakdown voltage of the photoelectric conversion element for each of the pixel circuits.

TECHNICAL FIELD

The present technology relates to a sensing device. Particularly, thepresent technology relates to a sensing device and an electronic devicecapable of detecting whether a photon is present or absent.

BACKGROUND ART

Conventionally, a distance measuring method called a time of flight(ToF) method has been used in an electronic device having a distancemeasuring function. The ToF method is a method in which a distance ismeasured by obtaining a round-trip time from emission of irradiationlight to an object from the electronic device until the irradiationlight is reflected and returns to the electronic device. For example,there has been proposed a solid-state imaging element that measures adistance using the ToF method, and controls an anode potential of asingle-photon avalanche diode (SPAD) on the basis of a variation insensitivity for each chip depending on a process or a temperature (forexample, see Patent Document 1). Here, the SPAD is a photodiodeimproving sensitivity by amplifying a photocurrent.

CITATION LIST Patent Document

Patent Document 1: Japanese Patent Application Laid-Open No. 2019-75394

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In the above-described conventional technology, the variation insensitivity for each chip is corrected by controlling an anodepotential. However, in the chip, the sensitivity may vary for each pixeldepending on a process or a temperature. In the above-describedsolid-state imaging element, the variation in sensitivity for each pixelcannot be corrected. For this reason, there is concern that thevariation in sensitivity between pixels may cause a distortion inbrightness and darkness in a distance image, resulting in a largevariation in distance measurement accuracy.

The present technology has been made in light of such a situation, andan object thereof is to provide a sensing device generating a distanceimage capable of reducing a variation in distance measurement accuracyin the distance image.

Solutions to Problems

The present technology has been made to solve the above-describedproblem. According to a first aspect of the present technology, asensing device includes: a predetermined number of pixel circuits eachincluding a photoelectric conversion element to which a predeterminedreverse bias voltage is applied between an anode and a cathode thereof,and a detection circuit that detects whether a photon is present orabsent on the basis of a potential of either the anode or the cathode;and a voltage control unit that adjusts the reverse bias voltage to avalue corresponding to a breakdown voltage of the photoelectricconversion element for each of the pixel circuits. This causes an effectthat a variation in sensitivity is corrected.

Furthermore, in the first aspect, the voltage control unit may include apredetermined number of individual bias circuits connected to thedifferent pixel circuits, respectively, to each supply a predeterminedindividual bias potential to one of the anode and the cathode. Thiscauses an effect that the individual bias potential is adjusted for eachpixel.

Furthermore, in the first aspect, the voltage control unit may furtherinclude a common bias circuit connected commonly to the predeterminednumber of pixel circuits to supply a predetermined common bias potentialto another one of the anode and the cathode. This causes an effect thatthe common bias potential is supplied to all the pixels.

Furthermore, in the first aspect, the individual bias circuit may supplythe individual bias potential to the cathode. This causes an effect thatthe potential of the cathode is adjusted.

Furthermore, in the first aspect, the individual bias circuit may supplythe individual bias potential to the anode. This causes an effect thatthe potential of the anode is adjusted.

Furthermore, in the first aspect, the pixel circuit and the individualbias circuit may be arranged in each of a predetermined number ofpixels. This causes an effect that the individual bias potential isadjusted for each pixel.

Furthermore, in the first aspect, the predetermined number of pixelcircuits may be dispersedly arranged in a plurality of pixel blocks, andthe individual bias circuit may be arranged in each of the plurality ofpixel blocks. This causes an effect that the individual bias potentialis adjusted for each pixel block.

Furthermore, in the first aspect, the predetermined number of pixelcircuits may be dispersedly arranged in a plurality of lines, and theindividual bias circuit may be arranged in each of the plurality oflines. This causes an effect that the individual bias potential isadjusted for each line.

Furthermore, in the first aspect, the individual bias circuit may bearranged at a position where heat distribution is not biased in a pixelarray unit. This causes an effect that heat is uniformly distributed.

Furthermore, in the first aspect, the sensing device may further includea voltage dividing resistor network in which a predetermined number ofnodes are connected to each other via resistors, the predeterminednumber of nodes may be connected to the different individual biascircuits, respectively, and each of the individual bias circuits maysupply the individual bias voltage corresponding to a reference voltagethat is a voltage of each of the nodes connected thereto. This causes aneffect that the individual bias potential for each pixel is supplied bya simple circuit.

Furthermore, in the first aspect, the sensing device may furtherinclude: a measurement value storage unit that stores a measurementvalue of the breakdown voltage of the photoelectric conversion elementfor each of the pixel circuits; and a setting unit that sets thereference voltage on the basis of the measurement value. This causes aneffect that the individual bias potential corresponding to themeasurement value of the breakdown voltage is supplied.

Furthermore, in the first aspect, the voltage control unit may performcontrol to hold an error of the breakdown voltage with respect to atarget value for each of the pixel circuits in the detection circuit,and apply a potential corresponding to the error to the anode. Thiscauses an effect that the reverse bias voltage corresponding to theerror of the breakdown voltage is applied.

Furthermore, in the first aspect, the detection circuit may include: apower reset switch that opens or closes a path between the cathode and apower potential; a capacitor inserted between the anode and a lowpotential lower than a predetermined reference potential; an anode resetswitch that opens or closes a path between both ends of the capacitor; acathode reset switch that opens or closes a path between the cathode andthe reference potential; and a logic gate that generates a pulse signalon the basis of a potential of the cathode. This causes an effect thatthe error of the breakdown voltage is held in the capacitor bycontrolling the switches.

In addition, in the first aspect, the voltage control unit maysequentially perform reset control of bringing the power reset switchinto an opened state and bringing the anode reset switch and the cathodereset switch into a closed state, holding control of bringing the powerreset switch and the anode reset switch into a closed state and bringingthe cathode reset switch into an opened state to hold the error in thecapacitor, and bias control of bringing the power reset switch into aclosed state and bringing the anode reset switch and the cathode resetswitch into an opened state to supply an excess bias to the cathode.This causes an effect that the excess bias is supplied after the erroris held.

Furthermore, according to a second aspect of the present technology, anelectronic device includes: a light emitting unit that suppliespredetermined irradiation light; a predetermined number of pixelcircuits each including a photoelectric conversion element to which apredetermined reverse bias voltage is applied between an anode and acathode thereof, and a detection circuit that detects whether a photonis present or absent in reflected light with respect to the irradiationlight on the basis of a potential of either the anode or the cathode;and a voltage control unit that adjusts the reverse bias voltage to avalue corresponding to a breakdown voltage of the photoelectricconversion element for each of the pixel circuits. This causes an effectthat a variation in sensitivity to light emitted by the light emittingunit is corrected.

Furthermore, according to a third aspect of the present technology, asensing device includes: a first pixel circuit including a firstphotoelectric conversion element, and a first detection circuit thatdetects whether a photon is present or absent on the basis of apotential of either an anode or a cathode of the first photoelectricconversion element; a second pixel circuit including a secondphotoelectric conversion element and a first detection circuit thatdetects whether a photon is present or absent on the basis of apotential of either an anode or a cathode of the second photoelectricconversion element; a first bias circuit connected to either the anodeor the cathode of the first photoelectric conversion element; a secondbias circuit connected to either the anode or the cathode of the secondphotoelectric conversion element; and a reference voltage supply unitthat supplies different reference voltages to the first and second biascircuits, respectively, to supply the potentials corresponding to therespective reference voltages. This causes an effect that differentpotentials are supplied for the respective pixel circuits.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of adistance measuring module in a first embodiment of the presenttechnology.

FIG. 2 is a diagram illustrating an example of a stack structure of asolid-state imaging element in the first embodiment of the presenttechnology.

FIG. 3 is a block diagram illustrating a configuration example of thesolid-state imaging element in the first embodiment of the presenttechnology.

FIG. 4 is a circuit diagram illustrating a configuration example betweena pixel and a common bias circuit in the first embodiment of the presenttechnology.

FIG. 5 is a diagram illustrating an arrangement example of circuits andelements for each chip in the first embodiment of the presenttechnology.

FIG. 6 is a block diagram illustrating a configuration example of asignal processing unit in the first embodiment of the presenttechnology.

FIG. 7 is a timing chart illustrating an example of fluctuations incathode potential and pulse signal in the first embodiment of thepresent technology.

FIG. 8 is a timing chart illustrating an example of a fluctuation incathode potential in a comparative example.

FIG. 9 is a diagram illustrating an example of a distance image in whichsensitivity varies in the comparative example.

FIG. 10 is a circuit diagram illustrating a configuration example of areference voltage supply unit in the first embodiment of the presenttechnology.

FIG. 11 is a diagram illustrating a setting example of a referencevoltage in the first embodiment of the present technology.

FIG. 12 is a timing chart illustrating an example of a fluctuation incathode potential in the first embodiment of the present technology.

FIG. 13 is a diagram illustrating an example of sensitivity for eachpixel of the distance image in the first embodiment of the presenttechnology.

FIG. 14 is a diagram for explaining voltage control in the firstembodiment of the present technology.

FIG. 15 is a flowchart illustrating an example of a measurement processat the time of shipment in the first embodiment of the presenttechnology.

FIG. 16 is a flowchart illustrating an example of a distance measuringprocess in the first embodiment of the present technology.

FIG. 17 is a circuit diagram illustrating a configuration example of apixel in a first modification of the first embodiment of the presenttechnology.

FIG. 18 is a circuit diagram illustrating a configuration example of apixel block in a second modification of the first embodiment of thepresent technology.

FIG. 19 is a diagram illustrating an arrangement example of circuits andelements for each chip in the second modification of the firstembodiment of the present technology.

FIG. 20 is a circuit diagram illustrating a configuration examplebetween an individual bias circuit and a line in a third modification ofthe first embodiment of the present technology.

FIG. 21 is a diagram illustrating an arrangement example of circuits andelements for each chip in the third modification of the first embodimentof the present technology.

FIG. 22 is a diagram illustrating another arrangement example ofcircuits and elements for each chip in the third modification of thefirst embodiment of the present technology.

FIG. 23 is a circuit diagram illustrating a configuration example of apixel in a fourth modification of the first embodiment of the presenttechnology.

FIG. 24 is a circuit diagram illustrating a configuration example of apixel block in a fifth modification of the first embodiment of thepresent technology.

FIG. 25 is a block diagram illustrating a configuration example of asolid-state imaging element in a second embodiment of the presenttechnology.

FIG. 26 is a circuit diagram illustrating a configuration example of apixel according to the second embodiment of the present technology.

FIG. 27 is a circuit diagram illustrating an example of an equivalentcircuit of an SPAD in the second embodiment of the present technology.

FIG. 28 is a graph illustrating an example of voltage-currentcharacteristics of the SPAD in the second embodiment of the presenttechnology.

FIG. 29 is a timing chart illustrating an example of an operation of acontrol circuit in the second embodiment of the present technology.

FIG. 30 is a circuit diagram illustrating an example of a state of apixel circuit when an anode and a cathode are reset in the secondembodiment of the present technology.

FIG. 31 is a circuit diagram illustrating an example of a state of thepixel circuit when the reset of the anode is canceled in the secondembodiment of the present technology.

FIG. 32 is a circuit diagram illustrating an example of a state of thepixel circuit when an error is held in the second embodiment of thepresent technology.

FIG. 33 is a circuit diagram illustrating an example of a state of thepixel circuit when the reset of the cathode is canceled in the secondembodiment of the present technology.

FIG. 34 is a circuit diagram illustrating an example of a state of thepixel circuit when an excess bias voltage is applied in the secondembodiment of the present technology.

FIG. 35 is a circuit diagram illustrating an example of the pixelcircuit in a standby state in the second embodiment of the presenttechnology.

FIG. 36 is a timing chart illustrating an example of fluctuations incathode potential and pulse signal in the second embodiment of thepresent technology.

FIG. 37 is a flowchart illustrating an example of an operation of thesolid-state imaging element in the first embodiment of the presenttechnology.

FIG. 38 is a block diagram depicting an example of schematicconfiguration of a vehicle control system.

FIG. 39 is a diagram depicting an example of an installation position ofan imaging section.

MODE FOR CARRYING OUT THE INVENTION

Modes for carrying out the present technology (hereinafter referred toas embodiments) will be described below. The description will be givenin the following order.

1. First embodiment (an example in which a reverse bias for each pixelis adjusted by an individual bias potential)

2. Second embodiment (an example in which a reverse bias for each pixelis adjusted by a potential corresponding to an error of a breakdownvoltage)

3. Example of Application to Mobile Body

1. First Embodiment Configuration Example of Distance Measuring Module

FIG. 1 is a block diagram illustrating a configuration example of adistance measuring module 100 in a first embodiment of the presenttechnology. The distance measuring module 100 measures a distance to anobject, and includes a light emitting unit 110, a synchronizationcontrol unit 120, and a solid-state imaging element 200. The distancemeasuring module 100 is mounted on a smartphone, a personal computer, anin-vehicle device, or the like, and is used to measure a distance. Notethat the device with the distance measuring module 100 installed thereonis an example of an electronic device described in the claims.

The synchronization control unit 120 operates the light emitting unit110 and the solid-state imaging element 200 in synchronization with eachother. The synchronization control unit 120 supplies a clock signal of apredetermined frequency (e.g., 10 to 20 megahertz) as a light emissioncontrol signal CLKp to the light emitting unit 110 and the solid-stateimaging element 200 via signal lines 128 and 129, respectively.

The light emitting unit 110 supplies intermittent light as irradiationlight in synchronization with the light emission control signal CLKpfrom the synchronization control unit 120. For example, near-infraredlight or the like is used as the irradiation light.

The solid-state imaging element 200 receives reflected light withrespect to the irradiation light to measure a round- trip time from alight emission timing indicated by the light emission control signalCLKp to a timing at which the reflected light is received. Thesolid-state imaging element 200 calculates a distance to the object foreach pixel from the round-trip time, and generates and outputs adistance image in which distance data indicating the distance isarranged. Note that the solid-state imaging element 200 is an example ofa sensing device described in the claims.

Configuration Example of Solid-State Imaging Element

FIG. 2 is a diagram illustrating an example of a stack structure of thesolid-state imaging element 200 in the first embodiment of the presenttechnology. The solid-state imaging element 200 includes a circuit chip202 and a pixel chip 201 stacked on the circuit chip 202. These chipsare electrically connected through a connector such as a via. Note thatthe chips can also be connected to each other by a Cu-Cu bond or a bump,rather than the via.

FIG. 3 is a block diagram illustrating a configuration example of thesolid-state imaging element 200 in the first embodiment of the presenttechnology. The solid-state imaging element 200 includes a referencevoltage supply unit 210, a control circuit 221, a pixel array unit 222,a measurement value storage unit 223, a bias voltage setting unit 224, asignal processing unit 230, and a common bias circuit 240. Furthermore,in the pixel array unit 222, a plurality of pixels 300 are arrayed in atwo-dimensional lattice pattern.

The reference voltage supply unit 210 individually supplies a referencevoltage VREF for each pixel. The control circuit 221 sequentially drivesrows to output pulse signals.

The pixel 300 detects whether a photon is present or absent using anSPAD. The pixel 300 outputs a pulse signal indicating a detection resultto the signal processing unit 230.

The signal processing unit 230 calculates a distance by measuring around-trip time for each pixel on the basis of the pulse signal from thepixel 300 and the light emission control signal CLKp from thesynchronization control unit 120. The signal processing unit 230generates a distance image in which distance data indicating thedistance is arranged, and outputs the distance image to the outside.

The measurement value storage unit 223 holds a digital signal for eachpixel indicating a measurement value of a breakdown voltage of the SPADin each pixel. In addition, in the measurement value storage unit 223, atarget value to be used for the calculation of the bias voltage settingunit 224 is held as well as the measurement value. The target value willbe described later. As the measurement value storage unit 223, forexample, a non-volatile memory or a register is used.

The bias voltage setting unit 224 reads out the measurement value andthe target value for each pixel from the measurement value storage unit223, and sets an output voltage of each of the reference voltage supplyunit 210 and the common bias circuit 240 on the basis of the read-outvalues.

The common bias circuit 240 supplies a predetermined common biaspotential as an anode potential VA to all the pixels.

Configuration Example of Pixel and Common Bias Circuit

FIG. 4 is a circuit diagram illustrating a configuration example betweenthe pixel 300 and the common bias circuit 240 in the first embodiment ofthe present technology. Each of the pixels 300 includes an individualbias circuit 310 and a pixel circuit 320.

The individual bias circuit 310 generates a potential corresponding tothe reference voltage VREF from the reference voltage supply unit 210 asan individual bias potential VE, and supplies the generated individualbias potential VE to the pixel circuit 320 in the same pixel. Areference voltage supplied to a pixel 300 in an x-th row (x is aninteger of 1 to X) and a y-th column (y is an integer of 1 to Y) will bedenoted by VREFxy. Note that the individual bias circuit 310 for eachpixel is an example of each of first and second bias circuits describedin the claims.

The individual bias circuit 310 includes an operational amplifier 311, ap-channel metal oxide semiconductor (pMOS) transistor 312, and a currentsource 313. The pMOS transistor 312 and the current source 313 areconnected to each other in series between a power supply voltage VDDHand a reference potential VSSH.

In addition, one of two input terminals of the operational amplifier 311is connected to the reference voltage supply unit 210, and the other oneof the two input terminals of the operational amplifier 311 is connectedto a connection node between the pMOS transistor 312 and the currentsource 313. An output terminal of the operational amplifier 311 isconnected to a gate of the pMOS transistor 312. Further, a potential ofthe connection node between the pMOS transistor 312 and the currentsource 313 is supplied to a detection circuit 330 as an individual biaspotential VE. Hereinafter, an individual bias potential of a pixel 300in an x-th row and a y-th column will be denoted by VExy.

The pixel circuit 320 includes a detection circuit 330 and a SPAD 340.The detection circuit 330 includes a drive transistor 331 and a logicgate 332.

The drive transistor 331 opens or closes a path between a cathode of theSPAD 340 and the node of the individual bias potential VExy according toa drive signal GAT from the control circuit 221. When the pixel circuit320 is driven in Geiger mode, the control circuit 221 controls the drivetransistor 331 to a closed state using the drive signal GAT.

The logic gate 332 generates a pulse signal PDET indicating a result ofdetecting whether a photon is present or absent on the basis of acathode potential VC of the SPAD 340. For example, an inverter is usedas the logic gate 332. For example, the logic gate 332 outputs ahigh-level pulse signal PDET to the signal processing unit 230 in a casewhere the cathode potential VC is equal to or smaller than apredetermined threshold value, and outputs a low-level pulse signal PDETto the signal processing unit 230 in a case where the cathode potentialVC exceeds the predetermined threshold value.

Hereinafter, a drive signal to an x-th row will be denoted by GATx, anda cathode potential and a pulse signal of a pixel 300 in an x-th row anda y-th column will be denoted by VCxy and PDETxy, respectively.

In addition, the common bias circuit 240 includes a current source 241,an nMOS transistor 242, and an operational amplifier 243. The currentsource 241 and the nMOS transistor 242 are connected to each other inseries between the power supply voltage VDDH and the reference potentialVSSH.

Furthermore, a reference voltage VAREF from the bias voltage settingunit 224 is input to one of two input terminals of the operationalamplifier 243, and the other one of the two input terminals of theoperational amplifier 243 is connected to a connection node between thecurrent source 241 and the nMOS transistor 242. An output terminal ofthe operational amplifier 243 is connected to a gate of the nMOStransistor 242. Furthermore, a potential of the connection node betweenthe current source 241 and the nMOS transistor 242 is supplied to anodesof the SPADs 340 of all the pixels as a common bias potential (i.e., ananode potential VA).

With the above-described configuration, in each of the pixels, theindividual bias circuit 310 generates an individual bias potential VEcorresponding to the reference voltage VREFxy, and supplies thegenerated individual bias potential VE to the corresponding pixelcircuit 320. Furthermore, the common bias circuit 240 supplies a commonbias potential (an anode potential VA) corresponding to the referencevoltage VAREF to the anodes of the SPADs 340 of all the pixels.

In addition, in the Geiger mode, a voltage between the individual biaspotential VExy and the anode potential VA is applied as a reverse biasvoltage between the anode and the cathode of the SPAD 340. Then, when aphoton is incident on the pixel 300 in a state where the reverse biasvoltage is applied thereto, the SPAD 340 multiplies a charge obtained byphotoelectrically converting the photon in an avalanche to generate aphotocurrent. When the cathode potential VCxy of the SPAD 340 drops andbecomes equal to or smaller than the threshold value according to thephotocurrent, the logic gate 332 detects the photon and outputs ahigh-level pulse signal PDETxy.

Here, the pixels may vary in the breakdown voltage of the SPAD 340depending on a process or a temperature. Due to the variation inbreakdown voltage, the pixels vary in photon detection efficiency (PDE).For this reason, the individual bias circuit 310 supplies an individualbias potential VE corresponding to a breakdown voltage measurement valueof the corresponding pixel. For example, the lower the breakdownvoltage, the lower value to which the individual bias potential VE isadjusted. The individual bias potential makes it possible to apply areverse bias voltage having a value corresponding to the breakdownvoltage, thereby correcting a variation in PDE for each pixel.

Note that the detection circuit 330 can detect whether a photon ispresent or absent on the basis of a potential of the cathode of the SPAD340, but can also detect whether a photon is present or absent on thebasis of a potential of the anode of the SPAD 340.

FIG. 5 is a diagram illustrating an arrangement example of circuits andelements for each chip in the first embodiment of the presenttechnology. In the pixel chip 201, the SPAD 340 is arranged for eachpixel. On the other hand, in the circuit chip 202 on which the pixelchip 201 is disposed, the individual bias circuit 310 and the detectioncircuit 330 corresponding to the SPAD 340 are arranged under each of theSPADs 340.

Configuration Example of Signal Processing Unit

FIG. 6 is a block diagram illustrating a configuration example of thesignal processing unit 230 in the first embodiment of the presenttechnology. The signal processing unit 230 includes a time-to-digitalconverter (TDC) 231 and a distance data generation unit 232 for eachcolumn.

The TDC 231 measures a time from a light emission timing indicated by alight emission control signal CLKp to the start of production of a pulsesignal PDET from the corresponding column (i.e. a light receptiontiming). The TDC 231 supplies a digital signal indicating the measuredtime to the distance data generation unit 232.

The distance data generation unit 232 calculates a distance D to anobject. For each cycle based on a vertical synchronization signal VSYNChaving a frequency (e.g., 30 hertz) lower than the light emissioncontrol signal CLKp, the distance data generation unit 232 obtains amode value among times measured by the TDC 231 during each cycle as around-trip time dt. Then, the distance data generation unit 232calculates a distance D using the following equation and generatesdistance data indicating the distance D. Data in which the distance datafor each pixel is arranged is output as a distance image.

D=c×dt/2

In the above equation, c is a speed of light, of which the unit ismeters per second (m/s). Furthermore, the unit of the distance D is, forexample, meter (m), and the unit of the round-trip time dt is, forexample, second (s).

FIG. 7 is a timing chart illustrating an example of fluctuations incathode potential and pulse signal in the first embodiment of thepresent technology. In an initial state of the Geiger mode, theindividual bias potential VE is applied to the cathode of the SPAD 340.In this way, the cathode potential VC becomes the individual biaspotential VE. The anode potential VA of all the pixels is lower than thereference potential VSSH. At this time, a voltage between the individualbias potential VE and the anode potential VA is applied as a reversebias voltage VAC between the anode and the cathode of the SPAD 340. Thereverse bias voltage VAC is set to a voltage having an absolute valuelarger than that of a breakdown voltage VBD when an avalanche breakdownoccurs. A difference between the breakdown voltage VBD and the reversebias voltage VAC is called an excess bias voltage VEX.

When a photon is incident at timing TO, the SPAD 340 multiplies a chargeobtained by photoelectrically converting the photon in an avalanche togenerate a photocurrent. The cathode potential VC of the SPAD 340 dropsaccording to the photocurrent. Then, when the cathode potential VCbecomes equal to or smaller than a threshold value VT of the logic gate332 at timing T1, the logic gate 332 outputs a high-level pulse signalPDET. In this way, the incidence of the photon is detected. The cathodepotential VC drops to a bottom potential VS corresponding to the excessbias voltage VEX.

Then, when the cathode potential VC rises by recharging and exceeds thethreshold value VT at timing T2, the logic gate 332 returns the pulsesignal PDET to the low level. The cathode potential VC returns to theoriginal individual bias potential VE at timing T3.

As described above, the pixels may vary in breakdown voltage VBDdepending on a process or a temperature. In order to observe theinfluence of the variation, a comparative example is presented, in whichthe same potential VE′ is applied to the cathodes of all the pixels,rather than providing the individual bias circuit 310.

FIG. 8 is a timing chart illustrating an example of a fluctuation incathode potential in the comparative example. Attention is paid to threepixels of addresses (1, 1), (1, 2), and (1, 3). It is assumed that abreakdown voltage VBD11 at the address (1, 1) is larger than a breakdownvoltage VBD12 at the address (1, 2), and the breakdown voltage VBD12 islarger than a breakdown voltage VBD13 at the address (1, 3). In thiscase, since the initial potential VE′ of the cathode is the same (inother words, the reverse bias is the same) between the pixels, an excessbias voltage VEX11 at the address (1, 1) is smaller than an excess biasvoltage VEX12 at the address (1, 2). In addition, the excess biasvoltage VEX12 is smaller than an excess bias voltage VEX13 at theaddress (1, 3).

Due to the variation in excess bias voltage VEX, at the time when aphoton is incident, a drop amount of a cathode potential VC11 at theaddress (1, 1) is smaller than that of a cathode potential VC12 at theaddress (1, 2). Also, the drop amount of the cathode potential VC12 issmaller than that of a cathode potential VC13 at the address (1, 3). Asdescribed above, in the comparative example, the drop amount of thecathode potential varies, causing a variation in PDE for each pixel.

FIG. 9 is a diagram illustrating an example of a distance image in whichsensitivity varies in the comparative example. FIG. 9 illustrates adistance image 500 when light having a uniform luminance is incident onall the pixels. In the distance image 500, a pixel value is determinedbased on the PDE of the pixel. In FIG. 9 , a pixel with high PDE isrepresented by a light color, and a pixel with low PDE is represented bya dark color.

In a case where the pixels vary in breakdown voltage VBD depending on aprocess or a temperature, PDE varies between the pixels due to theinfluence of the variation in breakdown voltage. For example, a lowerleft address (X, 1) has low PDE, an upper right address (1, Y) has highPDE, and the PDE gradually increases from a lower left end to an upperright end. In the comparative example, the variation in PDE between thepixels is not corrected, and thus, the variation causes a distortion inbrightness and darkness in the distance image. This distortion is calledshading noise.

FIG. 10 is a circuit diagram illustrating a configuration example of thereference voltage supply unit 210 in the first embodiment of the presenttechnology. The reference voltage supply unit 210 includes a voltagedividing resistor network in which a plurality of nodes N are connectedto each other via resistors 211. The node N is provided for each pixel,and a node at an address (x, y) will be denoted by N_(xy).

In order to suppress the shading noise described above, the distancemeasuring module 100 measures a breakdown voltage VBD for each pixel inadvance at the time of product shipment or the like. At the time ofmeasurement, any one of the following three measurement methods isadopted.

(1) A method in which breakdown voltages VBD for the respective pixelsare measured by connecting a measurement circuit to the cathodes of theSPADs 340 of all the pixels.

(2) A method in which breakdown voltages VBD of some parts (e.g., fourcorners) of the pixel array unit 222 are measured, and breakdownvoltages VBD of the other parts of the pixel array unit 222 areestimated.

(3) A method in which replica pixels for measurement are separatelyprepared to measuring breakdown voltages VBD.

A digital signal indicating a measurement value for each pixel is heldin the measurement value storage unit 223. When activated, the biasvoltage setting unit 224 reads out a measurement value and a targetvalue from the measurement value storage unit 223, and sets an outputvoltage of each of the reference voltage supply unit 210 and the commonbias circuit 240 on the basis of the read-out values.

For example, as illustrated in FIG. 9 , in a case where the PDEgradually increases from the lower left address (X, 1) to the upperright address (1, Y), a breakdown voltage VBD is measured as graduallydecreasing from the lower left end to the upper right end. In this case,the bias voltage setting unit 224 supplies a predetermined input voltageVRB to a lower left node N_(X1) and supplies an input voltage VRA lowerthan the input voltage VRB to an upper right node N_(1Y). These inputvoltages VRA and VRB are generated by, for example, a digital-to-analogconverter (DAC).

Then, a divided voltage between the input voltage VRA and the inputvoltage VRB is generated at each of the nodes by the voltage dividingresistor network. When the input voltage VRA is lower than the inputvoltage VRB, the divided voltage gradually decreases from the upper leftend to the upper right end. The divided voltage at the node N_(xy) issupplied as a reference voltage VREFxy to the individual bias circuit310 at the address (x, y).

Note that a resistance value of each of the resistors 211 may bevariable. When the resistance value is variable, a set value of theresistance value is held in the resistor or the like, and the resistancevalue is controlled based on the set value.

Furthermore, in the reference voltage supply unit 210, the referencevoltage VREF for each pixel is generated by the voltage dividingresistor network, but the reference voltage VREF can also be generatedby a circuit other than the voltage dividing resistor network.

FIG. 11 is a diagram illustrating a setting example of the referencevoltage VREF in the first embodiment of the present technology. In acase where the PDE gradually increases from the lower left address(X, 1) to the upper right address (1, Y), a reference voltage VREF isset as gradually increasing from the upper right end to the lower leftend.

FIG. 12 is a timing chart illustrating an example of a fluctuation incathode potential in the first embodiment of the present technology. Asdescribed with reference to FIGS. 9 to 11 , since the reference voltageVREF is set to correspond to the breakdown voltage VBD, the individualbias potential VE correspond to the breakdown voltage VBD is applied tothe cathode of each of the pixels.

For example, it is assumed that a breakdown voltage VBD11 at the address(1, 1) is larger than a breakdown voltage VBD12 at the address (1, 2),and the breakdown voltage VBD12 is larger than a breakdown voltage VBD13at the address (1, 3). At this time, an individual bias potential VE11is supplied to the address (1, 1), the individual bias potential VE11being larger than an individual bias potential VE12 at the address (1,2). Also, the individual bias potential VE12 is supplied to the address(1, 2), the individual bias potential VE12 being larger than anindividual bias potential VE13 at the address (1, 3).

By applying these individual bias potentials, the excess bias voltageVEX becomes substantially the same between the pixels. Accordingly, atthe time when a photon is incident, the drop amount of the cathodepotential is substantially the same between the pixels, and the PDE isalso substantially the same between the pixels.

FIG. 13 is a diagram illustrating an example of sensitivity for eachpixel in the distance image in the first embodiment of the presenttechnology. FIG. 9 illustrates a distance image 500 when light having auniform luminance is incident on all the pixels.

In a case where the pixels vary in breakdown voltage VBD as in thecomparative example, shading noise occurs as illustrated in FIG. 9 . Inthis regard, in the distance measuring module 100, the reference voltageVREF is set to a value corresponding to the breakdown voltage VBD foreach pixel to adjust a bias potential as illustrated in FIG. 11 . As aresult, as illustrated in FIG. 13 , the PDE is uniform between thepixels, thereby suppressing shading noise. Therefore, it is possible toreduce variations in distance measurement accuracy in the distance image501.

FIG. 14 is a diagram for explaining voltage control in the firstembodiment of the present technology. Each of the pixel circuits 320includes an SPAD 340 and a detection circuit 330. In the Geiger mode, areverse bias voltage is applied between the anode and the cathode of theSPAD 340. The detection circuit 330 detects whether a photon is presentor absent on the basis of a potential of the cathode of the SPAD 340.

Furthermore, the individual bias circuit 310 is connected to each of thepixel circuits 320. The individual bias circuit 310 supplies anindividual bias potential VE (e.g., VE11 or VE12) to the correspondingpixel circuit 320. The individual biases VE11 and VE12 are suppliedbecause different reference voltages VREF11 and VREF12 are supplied tothe respective individual bias circuits 310, and outputs of the biascircuits are determined on the basis of the respective referencevoltages, as described above. On the other hand, the pixel circuits 320of all the pixels are commonly connected to the common bias circuit 240.The common bias circuit 240 supplies a common bias potential as an anodepotential VA to the anodes of the SPADs 340 of all the pixels.

While the common bias potential (the anode potential VA) is supplied tothe anodes of all the pixels, an individual bias potential VE issupplied to the cathode for each pixel. The individual bias potential VEis controlled to a value corresponding to a breakdown voltage of theSPAD 340 for each pixel.

A circuit including the individual bias circuit 310 and the common biascircuit 240 for each pixel functions as a voltage control unit 305 thatadjusts a reverse bias voltage between the anode and the cathode foreach pixel. By adjusting the reverse bias voltage between the anode andthe cathode for each pixel, a variation in PDE (in other words,sensitivity) for each pixel can be corrected to suppress shading noise.

Operation Example of Distance Measuring Module

FIG. 15 is a flowchart illustrating an example of a measurement processat the time of shipment in the first embodiment of the presenttechnology. The measurement process at the time of shipment is carriedout, for example, at the time of shipment. The distance measuring module100 measures a breakdown voltage VBD for each pixel (step S901), andwrites a measurement value together with a target value into themeasurement value storage unit 223 (step S902). For example, a targetvalue of the bottom potential VS and a target value of the excess biasvoltage VEX are written into the measurement value storage unit 223.After the step S902, the distance measuring module 100 ends themeasurement process at the time of shipment.

FIG. 16 is a flowchart illustrating an example of a distance measuringprocess in the first embodiment of the present technology. The distancemeasuring process is started, for example, when a predeterminedapplication for generating a distance image is executed after shipment.

The bias voltage setting unit 224 initializes an individual biaspotential VE and a common bias potential (an anode potential VA) (stepS911). Then, the bias voltage setting unit 224 reads out a measurementvalue of a breakdown voltage VBD for each pixel from the measurementvalue storage unit 223 (step S912), and reads out a target value VSt ofa bottom potential VS (step S913).

The bias voltage setting unit 224 calculates a statistic (an averagevalue VBDAv, a sum, or the like) of the breakdown voltages VBD for therespective pixels, and sets an anode potential VA satisfying thefollowing equation by controlling the common bias circuit 240 (stepS914).

VA=VSt−VBDAv  Equation 1

Furthermore, the bias voltage setting unit 224 reads out a target valueVEXt of an excess bias voltage VEX (step S915). Then, the bias voltagesetting unit 224 sets an individual bias potential VE for each pixelsatisfying the following equation by controlling the reference voltagesupply unit 210 (step S916).

VExy=VSxy+VEXt =(VA+VBDxy)+VEXt  Equation 2

A calculation result of Equation 1 is input to VA on the right side ofEquation 2. In addition, a measurement value of a breakdown voltage atthe address (x, y) is input to VBDxy on the right side of Equation 2.

The common bias circuit 240 starts the supply of the set anode potentialVA (step S917), and the individual bias circuit 310 starts the supply ofthe set individual bias potential VE (step S918). Then, the distancemeasuring module 100 starts measuring a distance (step S919). After thestep S919, the distance measuring module 100 ends the distance measuringprocess.

Note that, although it has been described that the same anode potentialVA is supplied to all the pixels, an individual anode potentialcorresponding to a breakdown voltage of each pixel can be supplied toeach pixel. In this case, a bias circuit similar to the common biascircuit 240 is provided for each pixel and connected to the anode ofeach pixel. Then, an individual anode potential is supplied for eachpixel, using the following expression instead of Equation 1.

VAxy=VSt−VBDxy

As described above, according to the first embodiment of the presenttechnology, since the voltage control unit 305 adjusts a reverse biasvoltage for each pixel to a value corresponding to a breakdown voltageof each pixel, it is possible to correct a variation in sensitivitycaused by a variation in breakdown voltage for each pixel. By correctingthe variation in sensitivity, shading noise can be suppressed, and thevariation in distance measurement accuracy in a distance image can bereduced.

First Modification

In the first embodiment described above, the common bias circuit 240applies a common bias potential to the anodes. In this configuration,however, the common bias circuit 240 is required, and a circuit scale ofthe distance measuring module 100 increases accordingly. A firstmodification of the first embodiment is different from the firstembodiment in that the common bias circuit 240 is not arranged in thesolid-state imaging element 200.

FIG. 17 is a circuit diagram illustrating a configuration example of apixel 300 in the first modification of the first embodiment of thepresent technology. In the first modification of the first embodiment,the common bias circuit 240 is not arranged, and a predetermined anodepotential VA is applied to the anodes of the SPADs 340 of all thepixels. By eliminating the common bias circuit 240, it is possible toreduce a circuit scale of the distance measuring module 100.

As described above, in the first modification of the first embodiment ofthe present technology, since the common bias circuit 240 is eliminated,the circuit scale of the distance measuring module 100 can be reduced.

Second Modification

In the first modification of the first embodiment described above, thevoltage control unit 305 adjusts an individual bias potential for eachpixel. In this configuration, however, it is necessary to arrange anindividual bias circuit 310 for each pixel, making it difficult toincrease the number of pixels. A second modification of the firstembodiment is different from the first modification of the firstembodiment in that an individual bias circuit 310 is arranged for eachpixel block in the solid-state imaging element 200.

FIG. 18 is a circuit diagram illustrating a configuration example of apixel block 306 in the second modification of the first embodiment ofthe present technology. In the second modification of the firstembodiment, the pixel array unit 222 is divided into a plurality ofpixel blocks 306. In each of the pixel blocks 306, a predeterminednumber of pixel circuits 320 and one individual bias circuit 310 arearranged. For example, four pixel circuits 320 in 2 rows×2 columns arearranged for each pixel block 306.

The individual bias circuit 310 is commonly connected to the pixelcircuits 320 in the same pixel block 306 to supply an individual biaspotential VE to those pixel circuits 320. In this way, the individualbias potential VE is adjusted for each pixel block 306. The individualbias VE is supplied for each pixel block because different referencevoltages VREF are supplied to the respective pixel blocks, and outputsof the bias circuits are determined on the basis of the respectivereference voltages.

FIG. 19 is a diagram illustrating an arrangement example of circuits andelements for each chip in the second modification of the firstembodiment of the present technology. As illustrated in FIG. 19 , apredetermined number (e.g., four) of detection circuits 330 andindividual bias circuits 310 are arranged for each pixel block 306 inthe circuit chip 202. In FIG. 19 , a region surrounded by a dotted lineindicates a region corresponding to the pixel block 306. By arrangingthe individual bias circuit 310 for each pixel block 306, it is possibleto reduce a circuit scale of each pixel as compared with that in a casewhere the individual bias circuit 310 is arranged for each pixel. As aresult, it is easy to increase the number of pixels.

As described above, in the second modification of the first embodimentof the present technology, since the individual bias circuit 310 isarranged for each pixel block 306, the circuit scale can be reduced ascompared with that in a case where the individual bias circuit 310 isarranged for each pixel.

Third Modification

In the first modification of the first embodiment described above, thevoltage control unit 305 adjusts an individual bias potential for eachpixel. In this configuration, however, it is necessary to arrange anindividual bias circuit 310 for each pixel, making it difficult toincrease the number of pixels. A third modification of the firstembodiment is different from the first modification of the firstembodiment in that an individual bias circuit 310 is arranged for eachline in the solid-state imaging element 200.

FIG. 20 is a circuit diagram illustrating a configuration example of apixel block 306 in the third modification of the first embodiment of thepresent technology. In the third modification of the first embodiment, aplurality of lines is arranged in the pixel array unit 222. In each ofthese lines, pixel circuits 320 are arranged in a predetermineddirection (e.g., a horizontal direction). Also, an individual biascircuit 310 is arranged for each line. The individual bias circuit 310is commonly connected to each of the pixel circuits 320 in thecorresponding line to supply an individual bias potential VE to thepixel circuits 320. In this way, the individual bias potential VE isadjusted for each line. Note that the pixel circuits 320 can also bearranged for each line in the vertical direction. The individual bias VEis supplied for each line because different reference voltages VREF aresupplied to the respective lines, and outputs of the bias circuits aredetermined on the basis of the respective reference voltages.

FIG. 21 is a diagram illustrating an arrangement example of circuits andelements for each chip in the third modification of the first embodimentof the present technology. As illustrated in FIG. 21 , an individualbias circuit 310 is arranged for each line in the circuit chip 202. InFIG. 21 , a region surrounded by a dotted line indicates a regioncorresponding to the line. By arranging the individual bias circuit 310for each line, it is possible to reduce a circuit scale of each pixel ascompared with that in a case where the individual bias circuit 310 isarranged for each pixel. As a result, it is easy to increase the numberof pixels.

Note that, as illustrated in FIG. 21 , if the individual bias circuit310 is arranged only on one side of the line, heat may be generated fromthe individual bias circuit 310 intensively at that location. Since thePDE may vary due to fluctuations in temperature, it is preferable thatheat distribution on the chip is uniform.

Therefore, the individual bias circuit 310 can be arranged at a positionwhere heat distribution is not biased. For example, as illustrated inFIG. 22 , individual bias circuits 310 can be arranged on both sides ofeach line. In this case, half of the pixels in the line are connected tothe right individual bias circuit 310, and the remaining pixels areconnected to the left individual bias circuit 310. Alternatively, anindividual bias circuit 310 may be arranged at one of both side ends(e.g., a left side end) of an odd-numbered line, and another individualbias circuit 310 may be arranged at the other of both side ends (e.g., aright side end) of an even-numbered line.

As described above, in the third modification of the first embodiment ofthe present technology, since the individual bias circuit 310 isarranged for each line, the circuit scale can be reduced as comparedwith that in a case where the individual bias circuit 310 is arrangedfor each pixel.

Fourth Modification

In the first modification of the first embodiment described above, theindividual bias circuit 310 supplies an individual bias potential VE tothe cathode. However, the individual bias circuit 310 can also supply anindividual bias potential to the anode. A fourth modification of thefirst embodiment is different from the first embodiment in that theindividual bias circuit 310 supplies an individual bias potential to theanode in the solid-state imaging element 200.

FIG. 23 is a circuit diagram illustrating a configuration example of apixel 300 in the fourth modification of the first embodiment of thepresent technology. In the fourth modification of the first embodiment,the individual bias circuit 310 supplies an individual bias potential VA(e.g., VA11 or VA12) to the anode of the SPAD 340. The individual biasesVA11 and VA12 are supplied because different reference voltages VREF11and VREF12 are supplied to the respective individual bias circuits 310,and outputs of the bias circuits are determined on the basis of therespective reference voltages. In this way, the potential of the anodeis adjusted for each pixel. On the other hand, a potential common to allthe pixels is applied as VE to the cathodes.

Note that a common bias circuit 240 can be further added. In this case,the common bias circuit 240 supplies the common bias potential as VE tothe cathodes of all the pixels.

As described above, according to the fourth modification of the firstembodiment of the present technology, since the individual bias circuit310 supplies an individual bias potential to the anode, the potential ofthe anode can be adjusted for each pixel.

Fifth Modification

In the fourth modification of the first embodiment described above, thevoltage control unit 305 adjusts an individual bias potential for eachpixel. In this configuration, however, it is necessary to arrange anindividual bias circuit 310 for each pixel, making it difficult toincrease the number of pixels. A fifth modification of the firstembodiment is different from the fourth modification of the firstembodiment in that an individual bias circuit 310 is arranged for eachpixel block in the solid-state imaging element 200.

FIG. 24 is a circuit diagram illustrating a configuration example of apixel block 306 in the fifth modification of the first embodiment of thepresent technology. The fifth modification of the first embodiment isdifferent from the fourth modification in that the pixel array unit 222is divided into a plurality of pixel blocks 306. In each of the pixelblocks 306, a predetermined number of pixel circuits 320 and oneindividual bias circuit 310 are arranged.

By arranging the individual bias circuit 310 for each pixel block 306,it is possible to reduce a circuit scale of each pixel as compared withthat in a case where the individual bias circuit 310 is arranged foreach pixel. As a result, it is easy to increase the number of pixels.

Note that an individual bias circuit 310 supplying an individual biaspotential to the anodes can be arranged for each line.

As described above, in the fifth modification of the first embodiment ofthe present technology, since the individual bias circuit 310 isarranged for each pixel block 306, the circuit scale can be reduced ascompared with that in a case where the individual bias circuit 310 isarranged for each pixel.

2. Second Embodiment

In the first embodiment described above, the solid-state imaging element200 sets an individual bias potential on the basis of a breakdownvoltage measured in advance at the time of shipment. However, a value ofthe breakdown voltage may fluctuate depending on temperature after theshipment. A second embodiment is different from the first embodiment inthat the solid-state imaging element 200 holds an error of a breakdownvoltage with respect to a target value for each pixel after shipment.

FIG. 25 is a block diagram illustrating a configuration example of asolid-state imaging element 200 in the second embodiment of the presenttechnology. In the second embodiment, a control circuit 221, a pixelarray unit 222, and a signal processing unit 230 are arranged in thesolid-state imaging element 200. In the pixel array unit 222, aplurality of pixels 300 is arrayed in a two-dimensional lattice pattern.

FIG. 26 is a circuit diagram illustrating a configuration example of apixel 300 according to the second embodiment of the present technology.In the second embodiment, an SAPD 340 and a detection circuit 350 arearranged in the pixel 300. The detection circuit 350 includes a powerreset switch 351, an anode reset switch 352, a capacitor 353, a lowpotential supply unit 354, a cathode reset switch 355, and an inverter356.

The power reset switch 351 opens or closes a path between a potential VEand a cathode of the SPAD 340 according to a power reset signal RESHfrom the control circuit 221. For example, a power potential is used asthe potential VE.

The capacitor 353 is inserted between the anode of the SPAD 340 and thelow potential supply unit 354. The low potential supply unit 354supplies a low potential VRLD lower than a predetermined referencepotential (e.g., 0 volt) to one end of the capacitor 353. The other endof the capacitor 353 is connected to the anode of the SPAD 340.

The anode reset switch 352 opens or closes a path between both ends ofthe capacitor 353 according to an anode reset signal RESAN from thecontrol circuit 221.

The cathode reset switch 355 opens or closes a path between the cathodeof the SPAD 340 and the reference potential according to a cathode resetsignal RESL from the control circuit 221.

For example, nMOS transistors are used as the power reset switch 351,the anode reset switch 352, and the cathode reset switch 355. In thiscase, each of the switches shifts to a closed state in response to ahigh-level signal, and shifts to an opened state in response to alow-level signal.

The inverter 356 generates a pulse signal PDET on the basis of apotential of the cathode of the SPAD 340. Note that the inverter 356 isan example of a logic gate described in the claims.

Note that the control circuit 221 is an example of a voltage controlunit described in the claims.

FIG. 27 is a circuit diagram illustrating an example of an equivalentcircuit of the SPAD 340 in the second embodiment of the presenttechnology. The equivalent circuit of the SPAD 340 is represented by,for example, a circuit in which a switch 341, an internal resistor 342,and a breakdown voltage supply unit 343 are connected to each other inseries between the anode and the cathode.

The switch 341 shifts to a closed state to generate a photocurrent whena photon is incident. The breakdown voltage supply unit 343 supplies abreakdown voltage.

According to the configuration illustrated in FIG. 27 , when a photon isincident, the switch 341 shifts to a closed state, and a photocurrentflows through the internal resistor 342. As a result, the potential ofthe cathode drops.

FIG. 28 is a graph illustrating an example of voltage-currentcharacteristics of the SPAD 340 in the second embodiment of the presenttechnology. In FIG. 28 , the horizontal axis represents a voltageapplied between the anode and the cathode of the SPAD 340, and thevertical axis represents a photocurrent from the SPAD 340. In a case ofoperating in the Geiger mode, a voltage at a negative value, that is, areverse bias voltage is applied as the voltage between the anode andcathode of the SPAD 340. When the reverse bias voltage is lower than apredetermined breakdown voltage, an avalanche breakdown occurs in theSPAD 340, and a photocurrent is amplified. When a voltage lower than thebreakdown voltage by several volts is applied between the anode and thecathode, the gain in the amplification becomes substantially infinite,and one photon can be detected.

FIG. 29 is a timing chart illustrating an example of an operation of thecontrol circuit 221 in the second embodiment of the present technology.At timing T11 before the shift to the Geiger mode, the control circuit221 supplies a high-level anode reset signal RESAN over a pulse periodwhile setting the cathode reset signal RESL to a high level. At thistime, the power reset signal RESH is at a low level.

By the control at the timing T1, for example, a predetermined referencepotential (e.g., 0 volt) is applied to the cathode of the SPAD 340.

Then, at timing T12 when the pulse period has elapsed, the anode of theSPAD 340 reaches a predetermined low potential VRLD (e.g., −24 volts). Avoltage (e.g., −24 volts) between the anode and the cathode at this timecorresponds to a target value VBD₀ of the breakdown voltage.

Then, at timing T13, the light emitting unit 110 emits test light formeasuring an error of the breakdown voltage for each pixel with respectto the target value VBD₀. At the time of emitting the test light, asubject (e.g., white paper) having uniform reflectance is provided infront of the distance measuring module 100, such that light reflected bythe subject is incident on the solid-state imaging element 200.Alternatively, light from the outside of the distance measuring module100 is blocked, and the test light from the light emitting unit 110 isreflected in the distance measuring module 100, such that the reflectedlight is incident on the solid-state imaging element 200.

The cathode potential VC of the SPAD 340 rises by the incident light andbecomes, for example, −20 volts (V). Since no excess bias voltage isapplied, a breakdown voltage VBD_(m) occurs in each pixel between theanode and the cathode for the pixel. The pixels may vary in breakdownvoltage VBD_(m) due to a fluctuation in process or temperature, but anerror (e.g., +4 volts) of the breakdown voltage VBD_(m) with respect tothe target value VBD₀ is held in the capacitor 353 for each pixel.

Then, at timing T14, the control circuit 221 cancels the reset of thecathode by returning the cathode reset signal RESL to the low level.

At timing T15 immediately after the timing T14, the control circuit 221supplies a high-level power reset signal RESH over a pulse period. Bythis control, a potential VE (e.g., 3 volts) is applied to the anode ofthe SPAD 340. A voltage (e.g., 3 volts) between the potential VE and thereference potential is an excess bias voltage.

At the timing T15, the anode of the SPAD 340 remains at the potential(e.g., −20 volts) with the error (e.g., +4 volts). Therefore, a reversebias voltage (e.g. 23 volts) between the potential (e.g., −20 volts)with the error and the potential VE (e.g., 3 volts) is applied betweenthe anode and the cathode. That is, the reverse bias voltage is adjustedto a value corresponding to the breakdown voltage VBD_(m) for eachpixel.

At timing T16, the control circuit 221 returns the power reset signalRESH to the low level. The pixel circuit 320 shifts to the Geiger modein which a photon is awaited to be incident. When a photon is incidentin the Geiger mode, the potential of the anode drops.

FIG. 30 is a circuit diagram illustrating an example of a state of thepixel circuit 320 when the anode and the cathode are reset in the secondembodiment of the present technology. FIG. 30 illustrates a state of thepixel circuit 320 at the timing T11 of FIG. 29 .

At the timing T11, the control circuit 221 controls the power resetswitch 351 to be an opened state using a power reset signal RESH.Furthermore, the control circuit 221 controls both the anode resetswitch 352 and the cathode reset switch 355 to be a closed state usingan anode reset signal RESAN and a cathode reset signal RESL,respectively.

When the cathode reset switch 355 is in the closed state, the cathode ofthe SPAD 340 is initialized to a reference potential (e.g. 0 volt).Furthermore, when the anode reset switch 352 is in the closed state, alow potential VRLD (e.g., −24 volts) is applied to the anode of the SPAD340. At this time, a voltage (e.g., −24 volts) applied between the anodeand the cathode corresponds to a target value VBD₀ of the breakdownvoltage.

FIG. 31 is a circuit diagram illustrating an example of a state of thepixel circuit when the reset of the anode is canceled in the secondembodiment of the present technology. FIG. 31 illustrates a state of thepixel circuit 320 at the timing T12 of FIG. 29 .

At the timing T12, the control circuit 221 controls the anode resetswitch 352 to be an opened state using an anode reset signal RESAN.

FIG. 32 is a circuit diagram illustrating an example of a state of thepixel circuit 320 when an error is held in the second embodiment of thepresent technology. FIG. 32 illustrates a state of the pixel circuit 320at the timing T13 of FIG. 29 .

At the timing T13, reflected light of test light is incident. The anodepotential VA of the SPAD 340 rises by the incident light and becomes,for example, −20 volts (V). Since no excess bias voltage is applied, abreakdown voltage VBD_(m) occurs in each pixel between the anode and thecathode for the pixel. An error (e.g., +4 volts) of the breakdownvoltage VBD_(m) with respect to the target value VBD₀ is held in thecapacitor 353 for each pixel.

FIG. 33 is a circuit diagram illustrating an example of a state of thepixel circuit 320 when the reset of the cathode is canceled in thesecond embodiment of the present technology. FIG. 33 illustrates a stateof the pixel circuit 320 at the timing T14 of FIG. 29 .

At the timing T14, the control circuit 221 controls the cathode resetswitch 355 to be an opened state using a cathode reset signal RESL tocancel the reset of the cathode.

FIG. 34 is a circuit diagram illustrating an example of a state of thepixel circuit when an excess bias voltage is applied in the secondembodiment of the present technology. FIG. 34 illustrates a state of thepixel circuit 320 at the timing T15 of FIG. 29 .

At the timing T15, the control circuit 221 controls the power resetswitch 351 to be a closed state using a power reset signal RESH. By thiscontrol, a potential VE (e.g., 3 volts) is applied to the anode of theSPAD 340. A voltage (e.g., 3 volts) between the potential VE and thereference potential is an excess bias voltage VEX.

At the timing T15, a reverse bias voltage (e.g. 23 volts) between apotential (e.g., −20 volts) with an error and a potential VE (e.g., 3volts) is applied between the anode and the cathode.

FIG. 35 is a circuit diagram illustrating an example of the pixelcircuit 320 in a standby state in the second embodiment of the presenttechnology. FIG. 35 illustrates a state of the pixel circuit 320 at thetiming T16 of FIG. 29 .

At the timing T16, the control circuit 221 controls the power resetswitch 351 to be an opened state using a power reset signal RESH. Thepixel circuit 320 shifts to a state in which a photon is awaited to beincident (that is, the Geiger mode).

FIG. 36 is a timing chart illustrating an example of fluctuations incathode potential and pulse signal in the second embodiment of thepresent technology. In the Geiger mode, a reverse bias voltage VAC,which corresponds to a difference between the breakdown voltage VBD andthe excess bias voltage VEX, is applied between the anode and thecathode of the SPAD 340.

When a photon is incident immediately before timing T20, an avalanchebreakdown occurs in the SPAD 340, and the cathode potential VC drops.When the cathode potential VC becomes equal to or smaller than athreshold value VT at the timing T20, the detection circuit 350 outputsa high-level pulse signal PDET. Then, when the cathode potential VCrises by recharging and exceeds the threshold value VT at timing T21,the detection circuit 350 returns the pulse signal PDET to the lowlevel.

FIG. 37 is a flowchart illustrating an example of an operation of thesolid-state imaging element in the first embodiment of the presenttechnology. This operation is started, for example, before the shift tothe Geiger mode.

First, the control circuit 221 controls both the anode reset switch 352and the cathode reset switch 355 to be a closed state to initializespotentials of the anode and the reset (step S951).

The control circuit 221 controls the anode reset switch 352 to be anopened state to cancel the reset of the anode (step S952).

Then, when light is incident, the capacitor 353 holds an error of abreakdown voltage VBD_(m) (step S953).

The control circuit 221 controls the cathode reset switch 355 to be anopened state to cancel the reset of the cathode (step S954). The controlcircuit 221 controls the power reset switch 351 to be a closed state toapply an excess bias voltage VEX (step S955). The control circuit 221controls the power reset switch 351 to be an opened state to shift to astandby state for a photon (Geiger mode) (step S956). After the stepS956, a distance image is captured, and the solid-state imaging element200 ends the operation for capturing the distance image.

Note that the first embodiment and any of the first to fifthmodifications of the first embodiment can be applied to the secondembodiment. By adjusting an individual bias potential for each pixel, itis possible to further improve accuracy in correcting a variation inPDE.

As described above, in the second embodiment of the present technology,since the control circuit 221 performs control to hold an error of thebreakdown voltage VBD_(m) in the capacitor 353 and apply a potentialcorresponding to the error to the anode, a reverse bias voltage can beadjusted to a value corresponding to the breakdown voltage VBD_(m). As aresult, shading noise caused by variations in breakdown voltage can besuppressed, and the variation in distance measurement accuracy in adistance image can be reduced.

3. Application Example to Mobile Body

The technology according to the present disclosure (the presenttechnology) can be applied to various products. For example, thetechnology according to the present disclosure may be achieved as adevice mounted on any type of mobile body such as a vehicle, an electricvehicle, a hybrid electric vehicle, a motorcycle, a bicycle, a personalmobility, an airplane, a drone, a ship, or a robot.

FIG. 38 is a block diagram depicting an example of schematicconfiguration of a vehicle control system as an example of a mobile bodycontrol system to which the technology according to an embodiment of thepresent disclosure can be applied.

The vehicle control system 12000 includes a plurality of electroniccontrol units connected to each other via a communication network 12001.In the example depicted in FIG. 38 , the vehicle control system 12000includes a driving system control unit 12010, a body system control unit12020, an outside-vehicle information detecting unit 12030, anin-vehicle information detecting unit 12040, and an integrated controlunit 12050. In addition, a microcomputer 12051, a sound/image outputsection 12052, and a vehicle-mounted network interface (I/F) 12053 areillustrated as a functional configuration of the integrated control unit12050.

The driving system control unit 12010 controls the operation of devicesrelated to the driving system of the vehicle in accordance with variouskinds of programs. For example, the driving system control unit 12010functions as a control device for a driving force generating device forgenerating the driving force of the vehicle, such as an internalcombustion engine, a driving motor, or the like, a driving forcetransmitting mechanism for transmitting the driving force to wheels, asteering mechanism for adjusting the steering angle of the vehicle, abraking device for generating the braking force of the vehicle, and thelike.

The body system control unit 12020 controls the operation of variouskinds of devices provided to a vehicle body in accordance with variouskinds of programs. For example, the body system control unit 12020functions as a control device for a keyless entry system, a smart keysystem, a power window device, or various kinds of lamps such as aheadlamp, a backup lamp, a brake lamp, a turn signal, a fog lamp, or thelike. In this case, radio waves transmitted from a mobile device as analternative to a key or signals of various kinds of switches can beinput to the body system control unit 12020. The body system controlunit 12020 receives these input radio waves or signals, and controls adoor lock device, the power window device, the lamps, or the like of thevehicle.

The outside-vehicle information detecting unit 12030 detects informationabout the outside of the vehicle including the vehicle control system12000. For example, the outside-vehicle information detecting unit 12030is connected with an imaging section 12031. The outside-vehicleinformation detecting unit 12030 makes the imaging section 12031 imagean image of the outside of the vehicle, and receives the imaged image.On the basis of the received image, the outside-vehicle informationdetecting unit 12030 may perform processing of detecting an object suchas a human, a vehicle, an obstacle, a sign, a character on a roadsurface, or the like, or processing of detecting a distance thereto.

The imaging section 12031 is an optical sensor that receives light, andwhich outputs an electric signal corresponding to a received lightamount of the light. The imaging section 12031 can output the electricsignal as an image, or can output the electric signal as informationabout a measured distance. In addition, the light received by theimaging section 12031 may be visible light, or may be invisible lightsuch as infrared rays or the like.

The in-vehicle information detecting unit 12040 detects informationabout the inside of the vehicle. The in-vehicle information detectingunit 12040 is, for example, connected with a driver state detectingsection 12041 that detects the state of a driver. The driver statedetecting section 12041, for example, includes a camera that images thedriver. On the basis of detection information input from the driverstate detecting section 12041, the in-vehicle information detecting unit12040 may calculate a degree of fatigue of the driver or a degree ofconcentration of the driver, or may determine whether the driver isdozing.

The microcomputer 12051 can calculate a control target value for thedriving force generating device, the steering mechanism, or the brakingdevice on the basis of the information about the inside or outside ofthe vehicle which information is obtained by the outside-vehicleinformation detecting unit 12030 or the in-vehicle information detectingunit 12040, and output a control command to the driving system controlunit 12010. For example, the microcomputer 12051 can perform cooperativecontrol intended to implement functions of an advanced driver assistancesystem (ADAS) which functions include collision avoidance or shockmitigation for the vehicle, following driving based on a followingdistance, vehicle speed maintaining driving, a warning of collision ofthe vehicle, a warning of deviation of the vehicle from a lane, or thelike.

In addition, the microcomputer 12051 can perform cooperative controlintended for automated driving, which makes the vehicle to travelautomatedly without depending on the operation of the driver, or thelike, by controlling the driving force generating device, the steeringmechanism, the braking device, or the like on the basis of theinformation about the outside or inside of the vehicle which informationis obtained by the outside-vehicle information detecting unit 12030 orthe in-vehicle information detecting unit 12040.

In addition, the microcomputer 12051 can output a control command to thebody system control unit 12020 on the basis of the information about theoutside of the vehicle which information is obtained by theoutside-vehicle information detecting unit 12030. For example, themicrocomputer 12051 can perform cooperative control intended to preventa glare by controlling the headlamp so as to change from a high beam toa low beam, for example, in accordance with the position of a precedingvehicle or an oncoming vehicle detected by the outside-vehicleinformation detecting unit 12030.

The sound/image output section 12052 transmits an output signal of atleast one of a sound and an image to an output device capable ofvisually or auditorily notifying information to an occupant of thevehicle or the outside of the vehicle. In the example of FIG. 38 , anaudio speaker 12061, a display section 12062, and an instrument panel12063 are illustrated as the output device. The display section 12062may, for example, include at least one of an on-board display and ahead-up display.

FIG. 39 is a diagram depicting an example of the installation positionof the imaging section 12031.

In FIG. 39 , the imaging section 12031 includes imaging sections 12101,12102, 12103, 12104, and 12105.

The imaging sections 12101, 12102, 12103, 12104, and 12105 are, forexample, disposed at positions on a front nose, sideview mirrors, a rearbumper, and a back door of the vehicle 12100 as well as a position on anupper portion of a windshield within the interior of the vehicle. Theimaging section 12101 provided to the front nose and the imaging section12105 provided to the upper portion of the windshield within theinterior of the vehicle obtain mainly an image of the front of thevehicle 12100. The imaging sections 12102 and 12103 provided to thesideview mirrors obtain mainly an image of the sides of the vehicle12100. The imaging section 12104 provided to the rear bumper or the backdoor obtains mainly an image of the rear of the vehicle 12100. Theimaging section 12105 provided to the upper portion of the windshieldwithin the interior of the vehicle is used mainly to detect a precedingvehicle, a pedestrian, an obstacle, a signal, a traffic sign, a lane, orthe like.

Incidentally, FIG. 39 depicts an example of photographing ranges of theimaging sections 12101 to 12104. An imaging range 12111 represents theimaging range of the imaging section 12101 provided to the front nose.Imaging ranges 12112 and 12113 respectively represent the imaging rangesof the imaging sections 12102 and 12103 provided to the sideviewmirrors. An imaging range 12114 represents the imaging range of theimaging section 12104 provided to the rear bumper or the back door. Abird's-eye image of the vehicle 12100 as viewed from above is obtainedby superimposing image data imaged by the imaging sections 12101 to12104, for example.

At least one of the imaging sections 12101 to 12104 may have a functionof obtaining distance information. For example, at least one of theimaging sections 12101 to 12104 may be a stereo camera constituted of aplurality of imaging elements, or may be an imaging element havingpixels for phase difference detection.

For example, the microcomputer 12051 can determine a distance to eachthree-dimensional object within the imaging ranges 12111 to 12114 and atemporal change in the distance (relative speed with respect to thevehicle 12100) on the basis of the distance information obtained fromthe imaging sections 12101 to 12104, and thereby extract, as a precedingvehicle, a nearest three-dimensional object in particular that ispresent on a traveling path of the vehicle 12100 and which travels insubstantially the same direction as the vehicle 12100 at a predeterminedspeed (for example, equal to or more than 0 km/hour). Further, themicrocomputer 12051 can set a following distance to be maintained infront of a preceding vehicle in advance, and perform automatic brakecontrol (including following stop control), automatic accelerationcontrol (including following start control), or the like. It is thuspossible to perform cooperative control intended for automated drivingthat makes the vehicle travel automatedly without depending on theoperation of the driver or the like.

For example, the microcomputer 12051 can classify three-dimensionalobject data on three-dimensional objects into three-dimensional objectdata of a two-wheeled vehicle, a standard-sized vehicle, a large-sizedvehicle, a pedestrian, a utility pole, and other three-dimensionalobjects on the basis of the distance information obtained from theimaging sections 12101 to 12104, extract the classifiedthree-dimensional object data, and use the extracted three-dimensionalobject data for automatic avoidance of an obstacle. For example, themicrocomputer 12051 identifies obstacles around the vehicle 12100 asobstacles that the driver of the vehicle 12100 can recognize visuallyand obstacles that are difficult for the driver of the vehicle 12100 torecognize visually. Then, the microcomputer 12051 determines a collisionrisk indicating a risk of collision with each obstacle. In a situationin which the collision risk is equal to or higher than a set value andthere is thus a possibility of collision, the microcomputer 12051outputs a warning to the driver via the audio speaker 12061 or thedisplay section 12062, and performs forced deceleration or avoidancesteering via the driving system control unit 12010. The microcomputer12051 can thereby assist in driving to avoid collision.

At least one of the imaging sections 12101 to 12104 may be an infraredcamera that detects infrared rays. The microcomputer 12051 can, forexample, recognize a pedestrian by determining whether or not there is apedestrian in imaged images of the imaging sections 12101 to 12104. Suchrecognition of a pedestrian is, for example, performed by a procedure ofextracting characteristic points in the imaged images of the imagingsections 12101 to 12104 as infrared cameras and a procedure ofdetermining whether or not it is the pedestrian by performing patternmatching processing on a series of characteristic points representingthe contour of the object. When the microcomputer 12051 determines thatthere is a pedestrian in the imaged images of the imaging sections 12101to 12104, and thus recognizes the pedestrian, the sound/image outputsection 12052 controls the display section 12062 so that a squarecontour line for emphasis is displayed so as to be superimposed on therecognized pedestrian. The sound/image output section 12052 may alsocontrol the display section 12062 so that an icon or the likerepresenting the pedestrian is displayed at a desired position.

An example of the vehicle control system to which the technologyaccording to the present disclosure can be applied has been describedabove. The technology according to the present disclosure can be appliedto the outside-vehicle information detecting unit 12030 among thecomponents described above. Specifically, the distance measuring module100 of FIG. 1 can be applied to the outside-vehicle informationdetecting unit 12030. By applying the technology according to thepresent disclosure to the outside-vehicle information detecting unit12030, shading noise can be suppressed, and the variation in distancemeasurement accuracy in a distance image can be reduced.

Note that the above-described embodiments describe examples forembodying the present technology, and the matters in the embodiments andthe matters specifying the invention in the claims have a correspondencerelationship, respectively. Similarly, the matters specifying theinvention in the claims and the matters in the embodiments of thepresent technology denoted by the same terms as the matters specifyingthe invention have a correspondence relationship, respectively. However,the present technology is not limited to the embodiments, and can beembodied by making various modifications to the embodiments withoutdeparting from the gist thereof.

Note that the effects described in the present specification are merelyexamples and are not restrictive, and there may be other effects aswell.

Note that the present technology can also have the followingconfigurations.

(1) A sensing device, including:

a predetermined number of pixel circuits each including a photoelectricconversion element to which a predetermined reverse bias voltage isapplied between an anode and a cathode thereof, and a detection circuitthat detects whether a photon is present or absent on the basis of apotential of either the anode or the cathode; and

a voltage control unit that adjusts the reverse bias voltage to a valuecorresponding to a breakdown voltage of the photoelectric conversionelement for each of the pixel circuits.

(2) The sensing device according to (1), in which

the voltage control unit includes a predetermined number of individualbias circuits connected to the different pixel circuits, respectively,to each supply a predetermined individual bias potential to one of theanode and the cathode.

(3) The sensing device according to (2), in which

the voltage control unit further includes a common bias circuitconnected commonly to the predetermined number of pixel circuits tosupply a predetermined common bias potential to another one of the anodeand the cathode.

(4) The sensing device according to (2) or (3), in which

the individual bias circuit supplies the individual bias potential tothe cathode.

(5) The sensing device according to (2) or (3), in which

the individual bias circuit supplies the individual bias potential tothe anode.

(6) The sensing device according to any one of (2) to (5), in which

the pixel circuit and the individual bias circuit are arranged in eachof a predetermined number of pixels.

(7) The sensing device according to any one of (2) to (5), in which

the predetermined number of pixel circuits are dispersedly arranged in aplurality of pixel blocks, and

the individual bias circuit is arranged in each of the plurality ofpixel blocks.

(8) The sensing device according to any one of (2) to (5), in which

the predetermined number of pixel circuits are dispersedly arranged in aplurality of lines, and

the individual bias circuit is arranged in each of the plurality oflines.

(9) The sensing device according to (8), in which

the individual bias circuit is arranged at a position where heatdistribution is not biased in a pixel array unit.

(10) The sensing device according to any one of (2) to (9), furtherincluding

a voltage dividing resistor network in which a predetermined number ofnodes are connected to each other via resistors, in which

the predetermined number of nodes are connected to the differentindividual bias circuits, respectively, and

each of the individual bias circuits supplies the individual biasvoltage corresponding to a reference voltage that is a voltage of eachof the nodes connected thereto.

(11) The sensing device according to (10), further including:

a measurement value storage unit that stores a measurement value of thebreakdown voltage of the photoelectric conversion element for each ofthe pixel circuits; and

a setting unit that sets the reference voltage on the basis of themeasurement value.

(12) The sensing device according to (1), in which

the voltage control unit performs control to hold an error of thebreakdown voltage with respect to a target value for each of the pixelcircuits in the detection circuit, and apply a potential correspondingto the error to the anode.

(13) The sensing device according to (12), in which

the detection circuit includes:

a power reset switch that opens or closes a path between the cathode anda power potential;

a capacitor inserted between the anode and a low potential lower than apredetermined reference potential;

an anode reset switch that opens or closes a path between both ends ofthe capacitor;

a cathode reset switch that opens or closes a path between the cathodeand the reference potential; and

a logic gate that generates a pulse signal on the basis of a potentialof the cathode.

(14) The sensing device according to (13), in which

the voltage control unit sequentially performs reset control of bringingthe power reset switch into an opened state and bringing the anode resetswitch and the cathode reset switch into a closed state, holding controlof bringing the power reset switch and the anode reset switch into aclosed state and bringing the cathode reset switch into an opened stateto hold the error in the capacitor, and bias control of bringing thepower reset switch into a closed state and bringing the anode resetswitch and the cathode reset switch into an opened state to supply anexcess bias to the cathode.

(15) An electronic device, including:

a light emitting unit that supplies predetermined irradiation light;

a predetermined number of pixel circuits each including a photoelectricconversion element to which a predetermined reverse bias voltage isapplied between an anode and a cathode thereof, and a detection circuitthat detects whether a photon is present or absent in reflected lightwith respect to the irradiation light on the basis of a potential ofeither the anode or the cathode; and

a voltage control unit that adjusts the reverse bias voltage to a valuecorresponding to a breakdown voltage of the photoelectric conversionelement for each of the pixel circuits.

(16) A sensing device, including:

a first pixel circuit including a first photoelectric conversionelement, and a first detection circuit that detects whether a photon ispresent or absent on the basis of a potential of either an anode or acathode of the first photoelectric conversion element;

a second pixel circuit including a second photoelectric conversionelement and a first detection circuit that detects whether a photon ispresent or absent on the basis of a potential of either an anode or acathode of the second photoelectric conversion element;

a first bias circuit connected to either the anode or the cathode of thefirst photoelectric conversion element;

a second bias circuit connected to either the anode or the cathode ofthe second photoelectric conversion element; and

a reference voltage supply unit that supplies different referencevoltages to the first and second bias circuits, respectively, to supplythe potentials corresponding to the respective reference voltages.

REFERENCE SIGNS LIST

100 Distance measuring module

110 Light emitting unit

120 Synchronization control unit

200 Solid-state imaging element

201 Pixel chip

202 Circuit chip

210 Reference voltage supply unit

211 Resistor

221 Control circuit

222 Pixel array unit

223 Measurement value storage unit

224 Bias voltage setting unit

230 Signal processing unit

231 TDC

232 Distance data generation unit

240 Common bias circuit

241, 313 Current source

242 nMOS transistor

243, 311 Operational amplifier

300 Pixel

305 Voltage control unit

306 Pixel block

310 Individual bias circuit

312 pMOS transistor

320 Pixel circuit

330, 350 Detection circuit

331 Drive transistor

332 Logic gate

340 SPAD

341 Switch

342 Internal resistor

343 Breakdown voltage supply unit

351 Power reset switch

352 Anode reset switch

353 Capacitor

354 Low potential supply unit

355 Cathode reset switch

356 Inverter

1. A sensing device, comprising: a predetermined number of pixelcircuits each including a photoelectric conversion element to which apredetermined reverse bias voltage is applied between an anode and acathode thereof, and a detection circuit that detects whether a photonis present or absent on a basis of a potential of either the anode orthe cathode; and a voltage control unit that adjusts the reverse biasvoltage to a value corresponding to a breakdown voltage of thephotoelectric conversion element for each of the pixel circuits.
 2. Thesensing device according to claim 1, wherein the voltage control unitincludes a predetermined number of individual bias circuits connected tothe different pixel circuits, respectively, to each supply apredetermined individual bias potential to one of the anode and thecathode.
 3. The sensing device according to claim 2, wherein the voltagecontrol unit further includes a common bias circuit connected commonlyto the predetermined number of pixel circuits to supply a predeterminedcommon bias potential to another one of the anode and the cathode. 4.The sensing device according to claim 2, wherein the individual biascircuit supplies the individual bias potential to the cathode.
 5. Thesensing device according to claim 2, wherein the individual bias circuitsupplies the individual bias potential to the anode.
 6. The sensingdevice according to claim 2, wherein the pixel circuit and theindividual bias circuit are arranged in each of a predetermined numberof pixels.
 7. The sensing device according to claim 2, wherein thepredetermined number of pixel circuits are dispersedly arranged in aplurality of pixel blocks, and the individual bias circuit is arrangedin each of the plurality of pixel blocks.
 8. The sensing deviceaccording to claim 2, wherein the predetermined number of pixel circuitsare dispersedly arranged in a plurality of lines, and the individualbias circuit is arranged in each of the plurality of lines.
 9. Thesensing device according to claim 8, wherein the individual bias circuitis arranged at a position where heat distribution is not biased in apixel array unit.
 10. The sensing device according to claim 2, furthercomprising a voltage dividing resistor network in which a predeterminednumber of nodes are connected to each other via resistors, wherein thepredetermined number of nodes are connected to the different individualbias circuits, respectively, and each of the individual bias circuitssupplies the individual bias voltage corresponding to a referencevoltage that is a voltage of each of the nodes connected thereto. 11.The sensing device according to claim 10, further comprising: ameasurement value storage unit that stores a measurement value of thebreakdown voltage of the photoelectric conversion element for each ofthe pixel circuits; and a setting unit that sets the reference voltageon a basis of the measurement value.
 12. The sensing device according toclaim 1, wherein the voltage control unit performs control to hold anerror of the breakdown voltage with respect to a target value for eachof the pixel circuits in the detection circuit, and apply a potentialcorresponding to the error to the anode.
 13. The sensing deviceaccording to claim 12, wherein the detection circuit includes: a powerreset switch that opens or closes a path between the cathode and a powerpotential; a capacitor inserted between the anode and a low potentiallower than a predetermined reference potential; an anode reset switchthat opens or closes a path between both ends of the capacitor; acathode reset switch that opens or closes a path between the cathode andthe reference potential; and a logic gate that generates a pulse signalon a basis of a potential of the cathode.
 14. The sensing deviceaccording to claim 13, wherein the voltage control unit sequentiallyperforms reset control of bringing the power reset switch into an openedstate and bringing the anode reset switch and the cathode reset switchinto a closed state, holding control of bringing the power reset switchand the anode reset switch into a closed state and bringing the cathodereset switch into an opened state to hold the error in the capacitor,and bias control of bringing the power reset switch into a closed stateand bringing the anode reset switch and the cathode reset switch into anopened state to supply an excess bias to the cathode.
 15. An electronicdevice, comprising: a light emitting unit that supplies predeterminedirradiation light; a predetermined number of pixel circuits eachincluding a photoelectric conversion element to which a predeterminedreverse bias voltage is applied between an anode and a cathode thereof,and a detection circuit that detects whether a photon is present orabsent in reflected light with respect to the irradiation light on abasis of a potential of either the anode or the cathode; and a voltagecontrol unit that adjusts the reverse bias voltage to a valuecorresponding to a breakdown voltage of the photoelectric conversionelement for each of the pixel circuits.
 16. A sensing device,comprising: a first pixel circuit including a first photoelectricconversion element, and a first detection circuit that detects whether aphoton is present or absent on a basis of a potential of either an anodeor a cathode of the first photoelectric conversion element; a secondpixel circuit including a second photoelectric conversion element and afirst detection circuit that detects whether a photon is present orabsent on a basis of a potential of either an anode or a cathode of thesecond photoelectric conversion element; a first bias circuit connectedto either the anode or the cathode of the first photoelectric conversionelement; a second bias circuit connected to either the anode or thecathode of the second photoelectric conversion element; and a referencevoltage supply unit that supplies different reference voltages to thefirst and second bias circuits, respectively, to supply the potentialscorresponding to the respective reference voltages.